We will investigate the properties of the sodium, calcium and potassium selective current systems in isolated canine Purkinje cells. The cells are completely free of extracellular space restrictions and connective tissue and thus are reliable candidates for voltage clamp studies. We plan to use the free access to the cells to examine beta receptor density over the surface using iontophoretic isoproterenol. Additionally, we will test laser diffraction techniques to measure sarcomere dynamics in single cells under voltage clamp. The histology of the cells will be examined with the electron microscope.